Effects of multipurpose shopping trips on retail store location in a duopoly.

•We include multipurpose trips in location models for firms seeking sales maximizing.•Markets are significantly different to those using single purpose trips models.•We locate two firms’ stores selling different, possibly complementary products.•Customers purchase one, two or no product, depending on each action's utility.•A very efficient heuristic is proposed and tested, and extensive analysis is made of the solutions.